This invention relates to a locking device, and more particularly to a locking device which is automatically engageable or disengageable upon a change in pressure.
A particular application for such a locking device is as a security seal for use on passenger aircraft. The device can be used to seal the containers used for the in-flight distribution of perishable and non-perishable goods. The theft of goods from containers costs airlines vast sums of money each year. Although containers are sealed when they leave the warehouse, it is necessary for the seals to be easily removable by hand as it is quite impractical for cabin crews to carry special seal removal tools on the aircraft. We have found that these problems can be solved by a locking device which is pressure-sensitive; the device thus being actuated by the reduced pressure during flight.
The present invention thus provides a pressure-sensitive locking device comprising a housing having an opening therein, an insertable member adapted to be inserted into the housing through the opening, and a locking member in the housing, the locking member being biased towards engagement with the insertable member so that the locking member is lockably engageable with the insertable member upon insertion of the insertable member into the housing, and the locking member being cooperable with pressure-sensitive means pressure-sensitive arrangement in the housing to effect disengagement of the locking member from the insertable member upon a reduction of pressure.
In a preferred embodiment, the locking member is resiliently biased towards the insertable member when inserted in the housing so as to be in locking engagement therewith under normal atmospheric pressure. When the pressure is reduced, for example when an aircraft achieves a predetermined altitude, the pressure-sensitive means effects disengagement of the locking member from the insertable member, whereupon the insertable member can be withdrawn from the housing.
The opening in the housing preferably communicates with a channel, and the insertable member is preferably elongate and adapted to be slidingly inserted lengthwise through the opening into the channel.
The locking device can serve both as a barrier seal and as an indicative seal. The elongate member can be shaped so as to engage with a hasp or other securing device of an aircraft goods container. Alternatively, the elongate member can be U or J-shaped whereby the limbs can be inserted in two channels in the housing and lockable in one or both such channels, the device then being usable in the same way as a padlock. The locking device preferably includes an additional disposable locking element which engages with the elongate member in the locked position, and which has to be physically broken to permit withdrawal of the elongate member from the channel.